This invention relates to pneumatic and hydraulic actuators of the vane type. This invention further relates to vane type actuators having a clam shaped casing configuration. Actuators are known in the art as the mechanism used to open, close or position valves, dampers, doors, etc. Generally, they may be actuated with a hydraulic fluid or a pneumatic fluid such as air, nitrogen or a process gas. Actuators may be of the on/off variety or my be actuated to a range of positions through the use of a positioner.
Many vane actuator manufactures have settled on a casing design having a clam shaped configuration. For example, one of the leading sellers of vane type actuators, Kinetrol Ltd., has manufactured and sold a vane type actuator having a clam shaped configuration. This casing design is an optimal configuration for actuators having internal vanes of the paddle shaped variety. Other manufacturers such as Matryx and FMC have sold vane type actuators having similar configurations. The actuator case comprises case-halves, which are generally secured together with removable fasteners.
Actuators of the vane type design are very desirable since they may be designed to have only one moving part. This is accomplished by designing and manufacturing the actuator shaft and vane as a single machined piece. The vane is designed to have a minimal clearance between the internal surfaces of the case-halves. A seal may then be disposed on the peripheral surfaces of the vane to minimize leakage of a process fluid from one side of the vane to the other. The case-halves also include a port through which the shaft may extend. A seal may also be disposed between the shaft and the ports to minimize leakage of fluid.
One problem associated with prior art vane actuators is excess leakage of fluid from one side of the vane to the other. This prevents the actuator from maintaining the precise control over the component to be actuated or positioned. In a process plant such as a oil refinery or chemical plant, precise positioning of equipment such as a control valve or damper must be maintained to operate the facility efficiently or to prevent a catastrophic failure. While seal failures are one obvious source of excess leakage, more serious sources of excess leakage include high pressure excursions of the pneumatic or hydraulic fluid as well as expansion or contraction of the casing due to high and low temperatures. These latter sources of excessive leakage are especially notorious since such excursions may permanently damage the actuator often resulting in a loss of containment of the hydraulic or pneumatic fluid. Loss of containment of the pneumatic or hydraulic fluid can cause catastrophic system failures including loss of life and significant property damage.
Another problem associated with prior art vane actuators is that heretofore additional appurtenances were required to mount accessories such as solenoids, positioners, and limit switches. While international standards have been established by NAMUR for mounting accessories, vane actuator manufacturers have failed to design an actuator that complies with the NAMUR standards.
Therefore there is a need in the art for a vane actuator that reduces or eliminates excessive leakage due to high fluid pressures or excursions. There is a need in the art for a vane actuator that reduces or eliminates excessive leakage due to high or low operating temperatures. There is also a need in the art for a vane type actuator that meets NAMUR standards, thereby allowing accessories such as solenoids, limit switches and positioners of any manufacturer to be mounted directly to the vane actuator casing. A vane actuator which meets the above referenced needs is described herein below.